The driving wheels such as rear wheels of a FR (Front engine/Rear drive) vehicle, front wheels of a FF (Front engine/Front drive) vehicle and all wheels of a 4WD (4-wheel Drive) vehicle are supported by a suspension system via a wheel bearing apparatus. In recent years, there is a tendency to assemble the wheel hub, the constant velocity universal joint and the double row rolling bearing as a unit in order to reduce the weight and the size of the wheel bearing apparatus.
FIG. 14 is a longitudinal cross-section view of a prior art vehicle driving wheel bearing apparatus in which a wheel hub 50, a double row rolling bearing 60 and a constant velocity universal joint 70 are assembled as a unit. The wheel hub 50 is formed integrally with a wheel mounting flange 51 to mount a wheel (not shown). Hub bolts 52 to secure the wheel are equidistantly arranged along the periphery of the flange 51.
The double row rolling bearing 60 has an outer member 61, an inner member 62 and double row rolling elements 63 and 63. The outer member 61 has an integrally formed flange 64 to be mounted on a body of a vehicle (not shown) and double row outer raceway surfaces 61a and 61a formed on the inner surface. The inner member 62 has the wheel hub 50 and an outer joint member 71. The inner member 62 is formed with double row inner raceway surfaces 50a and 71a arranged respectively opposite to the outer raceway surfaces 61a and 61a of the outer member 61. The inner raceway surface 50a is formed on the outer circumferential surface of the wheel hub 50. The other raceway surface 71a is formed on the outer circumferential surface of the outer joint member 71 of the constant velocity universal joint 70. The double row rolling elements 63 and 63 are arranged between the outer raceway surfaces 61a and 61a and the inner raceway surfaces 50a and 71a. The rolling elements 63 and 63 are rotatably held by cages 65 and 65. Seals 66 and 67 are arranged at the ends of the double row rolling bearing 60 in order to prevent leakage of grease contained within the bearing and also to prevent ingress of rain water or dusts.
The constant velocity universal joint 70 has the outer joint member 71, a joint inner ring, a cage and torque transmission balls (not shown). The outer joint member 71 has a cup shaped mouth portion 72, a shaft portion 73 axially extending from the mouth portion 72, and axially extending curved track grooves 72a. The track grooves 72a are formed on the inner surface of the mouth portion 72.
The wheel hub 50 is formed with hardened irregular portion 53 on the inner circumferential surface. The wheel hub 50 and the outer joint member 71 are mutually connected by fitting the shaft portion 73 of the outer joint member 71 into the wheel hub 50. The fitting portion of the outer joint member 71 is radially outwardly expanded to cause plastic deformation of the outer joint member 71. This causes the hardened irregular portion 53 to bite into the outer circumferential surface at the fitting portion of the outer joint member 71 (see pages 4 and 5 and FIG. 1 of Japanese Laid-Open Patent Publication No. 18605/2001).
This type of connection structure, via the plastic deformation, can prevent loosening and abrasion of the fitted portion and thus can improve the durability and the driving stability. In addition, since the connection, via the plastic deformation, has both functions of torque transmission and connection of the wheel hub and the outer joint member, it is possible to achieve weight and size reduction of the apparatus.
In this type of wheel bearing apparatus, it is difficult to confirm the state of the connection between the wheel hub 50 and the outer joint member 71 due to the plastic deformation connection. Thus, the confirmation of the strength and endurance of the connected portion is carried out by a breakdown test via sampling inspection. Thus, it is desirable to further improve the quality and reliability of the connected portion.
For solving this problem, the applicant has proposed a vehicle wheel bearing apparatus shown in FIG. 13. In this bearing apparatus a hardened irregular portion 53 is formed on a radially outwardly arranged member (in this case the wheel hub 50′) at the fitted portion of the wheel hub 50′ and the outer joint member 71′. The wheel hub 50′ and the outer joint member 71′ integrally connected via plastic deformation of a radially inwardly arranged member (in this case the outer joint member 71′) by radially outwardly expanding the radially inwardly arranged member. This causes the hardened irregular portion of the radially outwardly arranged member to bite into the surface of the radially inwardly arranged member. The members are axially secured, via a caulked portion 74, formed by plastically deforming the end of the radially inwardly arranged member 71′ (see pages 3 and 4, FIG. 1 and FIG. 2 of Japanese Laid-Open Patent Publication No. 89301/2003).
However, such a bearing apparatus requires the caulking step or a retaining ring mount step in addition to the connecting step of the wheel hub 50′ and the outer joint member 71′ via plastic deformation. In recent years, the art has required not only compactness and light weightness of the bearing apparatus but an improvement of quality, reliability as well as low manufacturing cost.